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<title>Floating Types (Using the GNU Compiler Collection (GCC))</title>

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<h3 class="section" id="Additional-Floating-Types"><span>6.12 Additional Floating Types<a class="copiable-link" href="#Additional-Floating-Types"> &para;</a></span></h3>
<a class="index-entry-id" id="index-additional-floating-types"></a>
<a class="index-entry-id" id="index-_005fFloatn-data-types"></a>
<a class="index-entry-id" id="index-_005fFloatnx-data-types"></a>
<a class="index-entry-id" id="index-_005f_005ffloat80-data-type"></a>
<a class="index-entry-id" id="index-_005f_005ffloat128-data-type"></a>
<a class="index-entry-id" id="index-_005f_005fibm128-data-type"></a>
<a class="index-entry-id" id="index-w-floating-point-suffix"></a>
<a class="index-entry-id" id="index-q-floating-point-suffix"></a>
<a class="index-entry-id" id="index-W-floating-point-suffix"></a>
<a class="index-entry-id" id="index-Q-floating-point-suffix"></a>

<p>ISO/IEC TS 18661-3:2015 defines C support for additional floating
types <code class="code">_Float<var class="var">n</var></code> and <code class="code">_Float<var class="var">n</var>x</code>, and GCC supports
these type names; the set of types supported depends on the target
architecture.
Constants with these types use suffixes <code class="code">f<var class="var">n</var></code> or
<code class="code">F<var class="var">n</var></code> and <code class="code">f<var class="var">n</var>x</code> or <code class="code">F<var class="var">n</var>x</code>.  These type
names can be used together with <code class="code">_Complex</code> to declare complex
types.
</p>
<p>As an extension, GNU C and GNU C++ support additional floating
types, which are not supported by all targets.
</p><ul class="itemize mark-bullet">
<li><code class="code">__float128</code> is available on i386, x86_64, IA-64, and
hppa HP-UX, as well as on PowerPC GNU/Linux targets that enable
the vector scalar (VSX) instruction set.  <code class="code">__float128</code> supports
the 128-bit floating type.  On i386, x86_64, PowerPC, and IA-64
other than HP-UX, <code class="code">__float128</code> is an alias for <code class="code">_Float128</code>.
On hppa and IA-64 HP-UX, <code class="code">__float128</code> is an alias for <code class="code">long
double</code>.

</li><li><code class="code">__float80</code> is available on the i386, x86_64, and IA-64
targets, and supports the 80-bit (<code class="code">XFmode</code>) floating type.  It is
an alias for the type name <code class="code">_Float64x</code> on these targets.

</li><li><code class="code">__ibm128</code> is available on PowerPC targets, and provides
access to the IBM extended double format which is the current format
used for <code class="code">long double</code>.  When <code class="code">long double</code> transitions to
<code class="code">__float128</code> on PowerPC in the future, <code class="code">__ibm128</code> will remain
for use in conversions between the two types.
</li></ul>

<p>Support for these additional types includes the arithmetic operators:
add, subtract, multiply, divide; unary arithmetic operators;
relational operators; equality operators; and conversions to and from
integer and other floating types.  Use a suffix &lsquo;<samp class="samp">w</samp>&rsquo; or &lsquo;<samp class="samp">W</samp>&rsquo;
in a literal constant of type <code class="code">__float80</code> or type
<code class="code">__ibm128</code>.  Use a suffix &lsquo;<samp class="samp">q</samp>&rsquo; or &lsquo;<samp class="samp">Q</samp>&rsquo; for <code class="code">__float128</code>.
</p>
<p>In order to use <code class="code">_Float128</code>, <code class="code">__float128</code>, and <code class="code">__ibm128</code>
on PowerPC Linux systems, you must use the <samp class="option">-mfloat128</samp> option. It is
expected in future versions of GCC that <code class="code">_Float128</code> and <code class="code">__float128</code>
will be enabled automatically.
</p>
<p>The <code class="code">_Float128</code> type is supported on all systems where
<code class="code">__float128</code> is supported or where <code class="code">long double</code> has the
IEEE binary128 format.  The <code class="code">_Float64x</code> type is supported on all
systems where <code class="code">__float128</code> is supported.  The <code class="code">_Float32</code>
type is supported on all systems supporting IEEE binary32; the
<code class="code">_Float64</code> and <code class="code">_Float32x</code> types are supported on all systems
supporting IEEE binary64.  The <code class="code">_Float16</code> type is supported on AArch64
systems by default, on ARM systems when the IEEE format for 16-bit
floating-point types is selected with <samp class="option">-mfp16-format=ieee</samp> and,
for both C and C++, on x86 systems with SSE2 enabled. GCC does not currently
support <code class="code">_Float128x</code> on any systems.
</p>
<p>On the i386, x86_64, IA-64, and HP-UX targets, you can declare complex
types using the corresponding internal complex type, <code class="code">XCmode</code> for
<code class="code">__float80</code> type and <code class="code">TCmode</code> for <code class="code">__float128</code> type:
</p>
<div class="example smallexample">
<pre class="example-preformatted">typedef _Complex float __attribute__((mode(TC))) _Complex128;
typedef _Complex float __attribute__((mode(XC))) _Complex80;
</pre></div>

<p>On the PowerPC Linux VSX targets, you can declare complex types using
the corresponding internal complex type, <code class="code">KCmode</code> for
<code class="code">__float128</code> type and <code class="code">ICmode</code> for <code class="code">__ibm128</code> type:
</p>
<div class="example smallexample">
<pre class="example-preformatted">typedef _Complex float __attribute__((mode(KC))) _Complex_float128;
typedef _Complex float __attribute__((mode(IC))) _Complex_ibm128;
</pre></div>

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